class Solution {//leetcode695——岛屿的最大面积
private:
    int dx[4]={0,0,1,-1};
    int dy[4]={1,-1,0,0};
    void dfs(vector<vector<int>>& grid,int i,int j){
        cnt++;
        vis[i][j]=true;
        for(int k=0;k<4;k++){
            int x=i+dx[k];
            int y=j+dy[k];
            if(x>=0&&x<m&&y>=0&&y<n&&grid[x][y]==1&&vis[x][y]==false)
            dfs(grid,x,y);//右，左，上，下
        }
    }
public:
    int maxAreaOfIsland(vector<vector<int>>& grid) {
        m=grid.size();
        n=grid[0].size();
        vis.resize(m,vector<bool>(n,false));
        for(int i=0;i<m;i++){
            for(int j=0;j<n;j++){
                if(grid[i][j]==1&&!vis[i][j])
                {
                    dfs(grid,i,j);
                    ret=max(ret,cnt);
                    cnt=0;
                }
            }
        }
        return ret;
    }
private:
    int ret=0;
    int cnt=0;
    vector<vector<bool>> vis;
    int m;
    int n;
};